1. Field of Invention
The present invention relates to an ink composition for ink jet recording, which, even on various recording media having a low level of water absorption, especially synthetic paper and printing paper for running-on, can yield images having excellent gloss with good color reproduction, and a method for ink jet recording using the ink composition.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink are ejected and deposited on recording media, such as paper, to perform printing. An innovative advance of a recent ink jet recording technique has made it possible to realize, by ink jet recording, the production of images having quality comparable to images yielded by high-definition printing realized only by silver salt photography or offset printing. This trend has led to the development of inks for ink jet recording that can realize images having a high level of glossy impression comparable to the gloss of images produced by silver salt photography, using the so-called specialty papers which are recording media having a high level of gloss comparable to photographic paper, art paper and the like used in the field of silver salt photography and offset printing. Further, inks for ink jet recording which can realize image quality comparable to the image quality of images produced by silver salt photography even on plain paper, have also been developed.
Inks, which have been generally used for ink jet recording, are water-based inks that comprise water as a main component and a colorant and various additives. Regarding the colorant, the development of pigment-based inks utilizing the properties of the pigment has recently been forwarded because pigments are superior to dyes in weatherfastness properties such as lightfastness, gasfastness, waterfastness, and moisturefastness. For example, Japanese Patent Laid-Open No. 194500/2005 discloses a pigment-based ink having reduced feathering or bleeding properties and excellent gloss on specialty papers that have been realized by using a polysiloxane compound as a surfactant and adding an alkanediol such as 1,2-hexanediol as a solubilizer additive to the ink. Further, Japanese Patent Laid-Open No. 307184/2005 discloses that an ink, which has excellent ejection stability and can be evenly printed on recording media, can be produced by adding an alcohol having a specific chain length and an acetylene glycol surfactant to the ink.
The widespread use of techniques for forming images from digital data in recent years has led to an increased need for digital color proofs (DTPs) particularly in the field of printing, and an ink jet recording method has also become applied to DTPs. The color reproduction and stability reproduction of printed matters are required of DTPs. Accordingly, when proofs are prepared by the ink jet recording method, specialty paper for ink jet recording has been generally used.
In applications for color proof, however, ink jet recording on printing paper for running-on rather than specialty papers has been desired. Further, it is considered that proof cost can be significantly reduced if printed matter produced by ink jet recording directly on printing paper for running-on can be used as a final proof sample without use of any specialty paper.
The printing paper for running-on is a coated paper having on its surface a coating layer for receiving an oil-based ink. In the printing paper for running-on, however, the capability of the coating layer to absorb ink is disadvantageously poor. Therefore, when water-based pigment inks, which have been generally used in ink jet recording, are used, the penetrability of the inks into recording media (printing paper for running-on) is so low that feathering or bleeding or uneven coagulation sometimes occurs in images.
Further, in recent years, synthetic papers, which have been widely used in printing fields, produced by mixing an inorganic filler and the like into a polyethylene resin or a polyester resin and forming the mixture into a film have excellent recycle properties and have drawn attention as environmentally friendly materials.
Synthetic papers, however, generally have poor water absorption. Accordingly, when water-based inks are used, the ink overflows on a yielded image and sometimes causes feathering or bleeding or uneven coagulation as in the case of printing paper for running-on.